The present invention relates to a die-casting machine used for producing a cast article with molding material injected into a cavity formed by a pair of mold dies, specifically to the machine provided with double stage cylinders capable of injecting the material such as semisolid or thixotropic state of metal and boosting it in the cavity.
Conventionally, a die-casting machine with double stage cylinders, as shown in FIG. 5, is known, which is used for producing a cast article with molding material injected into a cavity formed by a pair of mold dies. This type of die-casting machine 90 is provided with a sleeve 14 through which a molding material 13 is injected into a cavity 12 formed by a pair of mold dies 11 and an injection plunger 15 slidably mounted in the sleeve 14, which pushes forward the molding material 13 supplied through an opening 16 into the sleeve 14.
The die-casting machine 9 is also provided with an injection cylinder 17 in which a piston 19 coupled through a piston rod 18 with the injection plunger 15 is slidably mounted and a boost cylinder 17A adjoining to the cylinder 17, in which a piston 20 for pressing the molding material 13 in the cavity 2 is slidably mounted.
To produce a cast article using the die-casting machine 90, the following two stage operations are necessary. The first stage is to supply pressurized oil to an oil chamber 19A on the head side of the injection cylinder 17 and to inject the molding material 13 into the cavity 12 by advancing the injection plunger 15 fixedly connected to the piston 19 of the injection cylinder 17. In the case, the molding material 13 is at first pushed forward in the sleeve 14 at low speed VL, as shown in FIG. 6, and then injected into the cavity 12 at high speed VH to avoid falling of temperature, immediately after the molding material 13 pushed out of the sleeve 14 reaches a gate 21.
After the molding material 13 is filled in the cavity 12 by advancing the injection plunger 15 at a position corresponding to completion of filling, the second stage starts. The second stage is to supply pressurized oil to the oil chamber 20A on the head side of the boost cylinder 17A so as to advance the piston 20 of the boost cylinder 17A, thereby holding to press and cool the molding material 13 filled in the cavity 12 until it becomes solid state.
As described above, the conventional type of die-casting machine 90 employs the two stage operations to produce the cast article. In case that the material to be cast in the cavity is fully liquid state like the molten metal, the conventional die-casting machine could produce any desired cast articles. However, in case that the material to be cast is semisolid or thixotropic state, the following problems arise. Firstly, in case of the semisolid or thixotropic state, because of a large flow resistance occurring when such semisolid or thixotropic state of metal to be cast passes through a narrow space like the gate 21, it is difficult to advance the injection plunger 15 at a desired speed, as the result, it takes much more time than expected to fill such material into the cavity 12. Therefore, the conventional die-casting machine 90 could not produce normal cast articles in case of semisolid or thixotropic state of metal to be cast. Secondly, to avoid such a problem, it may be proposed that the injection cylinder with large diameter for generating much more injection powers is employed. In the case, however, still another problem comes up, that is, the pressurized oil amount larger than that of the conventional machine is necessary for injection operation. For instance, even on the stroke operation at low injection speed VL in which only a small injection pressure needs, much more amount of oil has to be supplied by the quantity corresponding to the diameter enlargement of injection cylinder. Further, relating to the enlargement, characteristics of the injection cylinder on speed rising up, speed sloping, and boosting become worse, as the result, it becomes difficult to produce the cast article with high quality. Also, relating to the enlargement, total cost of the machine becomes expensive because of large sizing of the injection cylinder, the injection plunger and various hydraulic valves.
The object of the present invention is to provide a die-casting machine with double stage cylinders, which allows to operates a boost cylinder whenever it is required to keep enough injection power to be supplied, in accordance with increasing of flow resistance arising from a gate shape or formation and physical condition of molding material to be cast when the molding material reaches near the gate, especially capable of producing cast products with high quality even in case of semisolid or thixotropic state of metal as a material to be cast in a cavity.
More specifically, the present invention is arranged as follows:
A die-casting machine according to the present invention is provided with a sleeve through which cast material is injected into a cavity formed by a pair of mold dies, an injection plunger slidably mounted in the sleeve, an injection cylinder having an injection piston connected through a piston rod with the injection plunger, and a boost cylinder formed with an inner diameter larger than that of the injection cylinder and mounted adjacent to the injection cylinder thereon in a side opposite to the piston rod, wherein the injection cylinder and boost cylinder are communicated with a conduit connected to each hydraulic chamber on a rod side of the cylinders and connected to a flow rate control valve arranged on a side of meter-out with respect to the cylinders, thereby controlling a speed of the injection plunger in accordance with a flow rate of pressurized oil flowing in the valve.
In the die-casting machine of the present invention, there is further provided with a switching valve for controlling supplies of pressurized oil to a hydraulic chamber on a side of the piston in the boost cylinder. According to the above arrangement of the present invention, the switching valve is arranged so as to operate when the injection plunger reaches a predetermined stroke position during an injection operation.
According to still another arrangement of the present invention, a pilot operated servo valve may be employed as the switching valve.
In the above die-casting machine of the present inventions the boost cylinder is arranged to have a piston stroke equal to the injection plunger stroke corresponding to a volume of the cavity
In the above die-casting machine of the present invention, there is further provided with pressure sensors for detecting pressures in each oil chamber on both sides of a piston rod and a piston head in the injection cylinder, thereby judging whether the reaction force against the injection plunger exceeds a predetermined value, based on a difference in pressures detected by said pressure sensors, respectively.